This invention relates to a process for the production of low molecular weight unsaturated hydrocarbon polymers having an increased proportion of vinyl groups or substituted vinyl groups, respectively.
Several processes have been known for the production of low-molecular weight polybutadienes with a high (&gt;95%) 1,4-content and molecular weights of 500 to 50,000 (German Patents 1,186,631; 1,241,119; and 1,292,853). The products obtained according to this prior-art process are, however, not suitable for all purposes, due to their high 1,4-content. There is a real need for products having an increased proportion of vinyl groups.
It is known from German Published Application DAS 1,770,545 to produce 1,2-polybutadiene having a high percentage of vinyl configuration, by polymerizing butadiene in a halogenated hydrocarbon as the solvent with a catalyst containing as the essential component organic phosphines of the general formula PR'R"R"', wherein R' and R" are alkyl groups and R'" is an alkyl or aryl group. However, this process is burdened with deficiencies. On the one hand, the halogenated hydrocarbons, which represent the only solvent usable in this method, are very toxic. On the other hand, the phosphines are very expensive and moreover make it possible only with difficulty to produce polymers having molecular weights in the range of interest in varnish technology, viz., below 5,000.
It is an object of this invention to overcome the above-described disadvantages.